The invention relates particularly to a method for transmitting data in a CTI communications system in the 3rd party configuration.
CTI communications systems (CTI: Computer Telephony Integration) allow data interchange between telecommunications hardware, such as a telephone system, and a computer or a computer-protected software application. In terms of the arrangement of the telecommunications system and computer system, essentially two configurations are distinguished, the “1st party configuration” and the “3rd party configuration”.
In the 1st party configuration, a telephone is respectively connected directly to a computer. By contrast, in a CTI communications system in the 3rd party configuration, a network of telecommunications equipment communicates with a computer network via a server.
A typical example of a CTI communications system in the 3rd party configuration is shown in FIG. 1.
FIG. 1 shows a communications system 1 having a plurality of terminals 2a-2c connected thereto. These can be, as shown, telephones or any other type of data transmission equipment connected to the communications system 1 by an exchange line, such as fax machines.
The communications system 1 is connected by a data line 9 to a server 4, which is used as a TSP (Telephony Service Provider) and to which a plurality of client computers 3a-3c are in turn connected via an LAN (Local Area Network).
FIG. 2 shows the interconnection of the CTI communications system again in the form of a block diagram, with the interfaces between the individual blocks being shown.
As can be seen, the TSP 4 communicates with the communications system via a “CSTA interface” 8 (CSTA: Computer Supported Telephony Application interface) which defines the signal protocol between the server 4 and the telecommunications network 1. By contrast, the clients 3a-3c or the software applications 6a,6b running thereon for managing telecommunications-related data, which are also referred to as CTI or TAPI applications (TAPI: Telephony Application Programming Interface), communicate with the TSP 4 via a CTI interface 7. In the present example, the CTI interface is in the form of a TAPI interface.
With this system, a user of one of the clients 3a-3c can obtain particular prescribed information about a connection which is active in the communications system 1. This information can be, by way of example, the length of a telephone conversation conducted between two terminals 2a,2b, the subscribers involved in the conversation, charges etc., which are displayed to the user, for example in the software application running on his client 3a-3c. 
All the information and characteristic data relating to a communication connection are summarized in a “call”. This is an abstract unit which can be regarded as a data packet and has the prescribed contents, such as an identification number, the terminals 2a-2c involved in the connection, and other information relating to the connection.
Calls are always generated by the communications system 1 when a connection (call or conversation) has been set up between at least two terminals 2a-2c. 
A call model used in CTI communications systems is shown in FIG. 3 for the purpose of illustration. Accordingly, a call 5 storing data relating to the connection is shown between the terminals 2a-2c. 
This call 5 is transmitted via a data line 9 to the server 4, from where it is distributed further to prescribed clients 3a-3c. The information contained in the call is thus available on all the clients 3a-3c associated with the call.
Normally, a terminal 2a-2c has only one respective client 3a-3c associated with it, which means that the call is forwarded only to those clients 3a-3c which are associated with the call or with the terminals 2a-2c listed in the call.
The user of the client 3a is thus able, by way of example, to retrieve information about a conversation on the associated telephone 2a, but not on the telephone 2c. 
State changes in a communication connection, e.g. as a result of a conversation being ended or of another subscriber being added (conference call), are constantly monitored by the communications system 1 and an appropriately modified call is forwarded to the server 4. When a connection from a terminal 2a-2c is ended, the corresponding entry for the terminal (e.g. 2a) is erased in the call, so that the call is now associated only with the other clients. When a conversation between just two subscribers is ended, the associated call is erased completely.
Data transmission in this known CTI communications system has to date been limited to the transmission of information data relating to an ongoing connection. It has not been possible to transmit files between individual clients 3a-3c to date. It is also not possible to obtain information about those terminals 2a-2c which were involved in a call in the past and to implement a type of call tracking.
It is therefore one possible object of the present invention to allow data to be interchanged between the clients in a communications system.
The fundamental concept described below involves transmitting either entire files or data for call tracking (logging data) from a client to a TSP via the CTI interface and storing them in a prescribed memory area for an associated call. These files or data can then be read by another client associated with the call, likewise via the CTI interface.
In this case, logging data are to be understood to mean data which indicate which subscribers were involved in an existing connection in the past.
The files or logging data are thus transmitted between client and server in a simple manner using the already existing CTI interface, which means that no other interface needs to be opened.
To store the files or logging data in the associated call, it is necessary, as mentioned, for the call to have an additional memory area to which the data to be inserted can be written. This additional memory area can have a size of several KB, e.g. 64 KB.
In line with one preferred embodiment, the logging data comprise, by way of example, the length of a conversation, the subscribers involved in the conversation, or the type of connection (call, conversation or call forwarding etc.).
This allows a call to log information regarding all the terminals which were associated with this call over its entire course. For this purpose, each client or each CTI software application writes prescribed data relating to its associated terminal into the associated call. This is preferably done at the start and end of a connection (e.g. when ringing or after hanging up), so that at least the start and end of a connection are recorded.
When diverting a call or transferring from one terminal to another, each of the associated clients preferably enters data, particularly the subscriber or user on the associated terminal, into the associated call, so that ultimately a type of connection history is produced. Since this information is available to all the clients associated with the call, the connection history for this call is thus available to all (including recently added) associated clients. A subscriber recently added to an existing call is thus shown the connections active to date on his client computer.
The connection history comprises at least the names of the users of terminals with which the call has been associated to date. In addition, the connection history can contain data relating to the length of the connection, to the type of connection, to the date, time, etc.